Add copy task link button to task cards

[MeisnerDan]

Add a button to task cards and task detail pages that copies a deep link (e.g., mission-control.local/tasks/task_123456) to the clipboard. This allows users to share task references in messages, emails, or across collaboration tools. Include a brief toast notification confirming the copy action.

Acceptance Criteria

• Copy button appears on task cards and task detail pages
• Clicking the button copies the full task URL to clipboard
• Toast notification confirms successful copy ("Task link copied!")
• Toast disappears automatically after 3 seconds
• Works on both desktop and mobile (touch-friendly button size)
• Uses native Clipboard API with fallback for older browsers
• Unit tests verify URL generation and clipboard functionality